Further cleanup on cpv script;

[fghalasz]

1. add back a ln_or_cp function and use it to cp only when ln fails. Deploy t5his function for all instances of linking/copying in the script;
2. better handling of case where the unversioned destination file does not exist but versioned destination file DOES exist. In this case creates a new next higher versioned file. Previously, in this case just created a new unversioned file and did not create a new higher version file.
3. more informative error messages

[nbriggs]

Doesn't make Solaris happy, because /bin/sh does not support the "local" declarations, so an attempt to use cpv results in

% scripts/cpv /tmp/xxx /var/tmp/yyy
scripts/cpv[7]: local: not found [No such file or directory]
scripts/cpv[8]: local: not found [No such file or directory]
cp: Insufficient arguments (1)
Usage: cp [-f] [-i] [-p] [-P] [-z] [-@] [-/] f1 f2
       cp [-f] [-i] [-p] [-P] [-z] [-@] [-/] f1 ... fn d1
       cp -r [-H|-L|-P] [-f] [-i] [-p] [-z] [-@] [-/] d1 ... dn-1 dn
       cp -R [-H|-L|-P] [-f] [-i] [-p] [-z] [-@] [-/] d1 ... dn-1 dn
Error: failed to add yyy to /var/tmp

[masinter]

note that #1352 inconsistent

[fghalasz]

OK. Removed local declarations from cpv script to make it POSIX-compliant. Ready for re-review.

[masinter]

lgtm -- not sure why this wasn't reviewed before.